In many applications the noise generated by electrical motors can be a significant factor in the overall design. Commercial applications such as locomotives or cruise liners and military applications such as antisubmarine frigates put particular emphasis on noise and vibration levels. The calculation of these levels involves an understanding of the electrical/mechanical interaction of magnetic force and stator behaviour. Analysis of the vibration behaviour of electrical machines has, in the past, concentrated on identifying the natural frequencies and mode shapes of highly symmetrical machine stators, for example stators of small motors. In practice, however, it has been found that geometrical and constructional irregularities introduce asymmetrical behaviour, which results in an enriched frequency response spectrum. The paper describes the results of modal tests carried out on an induction motor stator, and discusses the effects of irregularities on the vibration response of the machine. Based on the experimental investigation, some new and useful conclusions are derived. The implications for machine design are also discussed.